The resurgence of interest in thoracic paravertebral block (TPVB) can be traced
back to a seminal article by Eason and Wyatt in 1979,1 although it was
first described by Selheim in 1906 and modified by Lawen in 1911.2
The conventional technique of TPVB involves inserting the needle perpendicular
to all planes, contacting the transverse process, and then walking off it with
the needle. The commonly-used endpoints for needle insertion include loss-of-resistance
to air or saline,1,2 advancing a pre-determined distance,3
or neurostimulation.4,5 Complications of TPVB are reportedly low,
with the most feared being pleural puncture and pneumothorax (1.1% and 0.5%
respectively in 1 study6).

Ultrasound has been used to enhance the safety and efficacy of TPVB by determining
the location and depth of the transverse process and the parietal pleura.7,8
Pusch et al8 performed a pre-procedure scan and then performed TPVB
in the conventional fashion using loss-of-resistance to saline as their endpoint.
Hara et al7 imaged the transverse process and the thoracic
paravertebral space (TPVS) in a longitudinal parasagittal plane during actual
block performance; however the needle was inserted out-of-plane to the probe
using a conventional technique, and loss-of-resistance to saline was used
as the endpoint for needle placement rather than ultrasonographic
visualization of needle-tip position.

Here we describe an in-plane ultrasound-guided technique that utilizes direct
visualization of needle-tip position and local anesthetic spread as the endpoint.
The approach is similar to one described by Kappis in 1912. In the original
description, a 10 cm needle was inserted three fingerbreadths from the midline
at a 45 degree angle to the skin, and advanced into the TPVS until the tip contacted
the thoracic vertebral body. The technique was eventually abandoned because of the
risk of needle penetration through the intervertebral foramen, and thus inadvertent
dural puncture and spinal cord injury. However ultrasonographic visualization
of in-plane needle advancement reduces the risk of pleural puncture as well as
entry of the needle into the intervertebral foramen. Nevertheless the
practitioner should be aware that there is a risk of epidural local anesthetic
spread with paravertebral injection.

Anatomy
The thoracic paravertebral space (TPVS), when viewed in transverse cross-section
is triangular-shaped (red triangle in figure below). The base is formed by the
posterolateral aspect of the vertebral body / intervertebral discs / intervertebral
foramina / articular processes. The anterolateral border is formed by the parietal
pleura, whilst the posterior border is formed by the superior costotransverse
ligament. This ligament extends from the inferior aspect of the transverse
process above to the superior aspect of the rib tubercle below. Lateral to
this ligament (and continuous with it) is the internal intercostal membrane,
which is the aponeurotic continuation of the internal intercostal muscle,
and thus runs between the upper and lower border of adjacent ribs.12
The apex of the triangular TPVS communicates with the intercostal space laterally.
The cephalad limit of the TPVS has not been defined. It has been shown
that solution injection into the TPVS can spread caudad into the
abdominal and lumbar region, through the medial and lateral arcuate
ligaments of the diaphragm. It is generally accepted, however, that
the caudad limit of the paravertebral space is at the origin of the psoas
muscle at L1.9

The TPVS contains mainly fatty tissue, and is traversed by the intercostal or
spinal nerves, intercostal vessels, dorsal rami, rami communicantes, and the
sympathetic chain. The spinal nerves do not have a fascial sheath in the TPVS,
which explains their susceptibility to local anesthetic blockade.

The space is divided into an anterior and posterior compartment by a fibroelastic
membrane, the endothoracic fascia. The endothoracic fascia is the deep investing
fascia of the thoracic cavity. It blends medially with the periosteum of the
vertebral body; and laterally, is closely applied to the ribs. Caudally,
it is continuous with the transversalis fascia of the abdominal cavity and
this may explain why solutions injected in the TPVS may spread to the
lumbar region. The spinal nerves have been described as running through
the compartment posterior to the endothoracic fascia.2 This
however is controversial,10,11 as the precise anatomy of the
endothoracic fascia, and its relationship to the spinal nerves in
particular, remains ill-defined. It has been shown that injection closer
to the spinal nerves (using a nerve-stimulator-guided technique) is more
likely to result in longitudinal spread of the injectate in the TPVS.11

Scanning Technique

Place the patient in one of the following positions to expose their
upper back: a) lateral decubitus position (surgical side uppermost);
b) prone position; c) sitting position.

After skin and transducer preparation
(see Preparing Transducer for Single Shot), place a linear 38 mm,
high frequency 10-12 MHz transducer in an axial (transverse) plane
on the rib at the selected thoracic level, just lateral to the
spinous process.

The transverse process and rib are visualized as a hyperechoic line with
acoustic shadowing below it (figure below).

Thoracic Paravertebral Space Localization

Move the transducer caudad into the intercostal space between adjacent ribs.

The transverse process can be visualized on the medial side as a
hyperechoic convex line with acoustic shadowing beneath (figure below).

The TPVS and the adjoining intercostal space can now be visualized
(figure below).

The TPVS is a wedge-shaped hypoechoic layer demarcated by the hyperechoic
lines of the pleura below and the internal intercostal membrane above.

Note that the pleura is clearly visible as a hyperechoic line that moves
with respiration and with underlying hyperechoic air artifacts. This
is distinctly different from the hyperechoic rib line with underlying
acoustic shadow.

It may be possible to identify intercostal vessels in the TPVS with
Color Doppler, and if so, these should be avoided.

Accurate needle tip visualization is ESSENTIAL at all times to avoid
inadvertent pleural puncture or entry into the intervertebral foramen.

In Plane Approach (Lateral to Medial)

Following local anesthetic infiltration of the skin, insert a 20-gauge
Tuohy needle at the outer (lateral) end of the transducer, IN-PLANE
with the ultrasound beam.

It is recommended that the bevel of the Tuohy needle tip be oriented
upwards towards the transducer as this may reduce the risk of
penetrating injury to intercostal vessels, nerve or pleura in the
event of inadvertent needle contact.

Advance the needle in-plane with the transducer, in a lateral-to-medial
direction.

Advance the needle (arrows, figure below) under real time ultrasound
guidance and visualize needle tip penetration through the internal
intercostal membrane and its entry into the TPVS.

A pop is often felt as the needle penetrates the internal intercostal
membrane.

Out of Plane Approach

The out of plane approach is an acceptable approach for this block.

Local Anesthetic Injection

After ensuring negative aspiration for blood, 15-20 mL of local
anesthetic is injected slowly in small increments into the TPVS.

The TPVS will be observed to distend, pushing the pleura downwards
(ventrally) (figure below).